A radiation image recording and reproducing method utilizing a stimulable phosphor as described, for instance, in U.S. Pat. No. 4,239,968, is now practically employed. In the method, a radiation image storage panel comprising a stimulable phosphor in the form of particles (i.e., stimulable phosphor sheet) is employed, and the method involves the steps of causing the stimulable phosphor of the storage panel to absorb energy of radiation having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to an object at a considerably smaller dose, as compared with a conventional radiography using a combination of a radiographic film and radiographic intensifying screen. Further, the radiation image recording and reproducing method using a stimulable phosphor is of greater value especially when the method is employed for medical diagnosis.
The radiation image storage panel employed in the above-described method comprises a stimulable phosphor layer which is optionally provided on a support. Further, a transparent layer of a polymer material is generally provided on the free surface (e.g., surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock.
The phosphor layer generally comprises a binder and a stimulable phosphor (in the form of particles) dispersed therein. The stimulable phosphor emits light (that is, given stimulated emission) when it is exposed to radiation such as X-rays and then excited with stimulating rays. Accordingly, the radiation having passed through an object or radiated from an object is absorbed by the stimulable phosphor layer of the storage panel in an amount proportional to the applied radiation dose, and a radiation image of the object is produced on the storage panel in the form of a radiation energy-stored image. The radiation energy-stored image is released as stimulated emission by sequentially irradiating the storage panel with stimulating rays. The stimulated emission is then photoelectrically detected to give a series of electric signals, so as to reproduce a visible image from the electric signals.
The radiation image recording and reproducing method is generally performed in a united radiation image recording and reading apparatus which comprises recording means (for applying a radiation having an image information to the radiation image storage panel to record the radiation image on the storage panel); reading means (for irradiating the stimulating rays to the storage panel having the radiation image to produce stimulated emission from the storage panel and photoelectrically reading the stimulated emission); erasing means (for applying an erasing light to the storage panel after the reading step is complete to remove a radiation image remaining in the storage panel); and transfer system (which is arranged between these means, for transferring the storage panel from one means to another means in predetermined order). Alternatively, the radiation image recording and reading apparatus may comprise two separate apparatuses, that is, a radiation image recording apparatus and a radiation image reading apparatus equipped with erasing means.
In any of the radiation image recording and reproducing systems, the radiation image storage panel is repeatedly employed after the remaining radiation image is erased.
In a representative radiation image reproducing method, the stimulable phosphor particles are sequentially excited by applying the stimulating rays to one surface of the radiation image storage panel, and then the produced light emission is photoelectrically detected from the surface to which the stimulating rays are applied.
In the radiation image recording and reproducing method, it is naturally desired to give a radiation image of good quality (such as a high sharpness and a high graininess).
U.S. Pat. No. 4,394,581 describes coloring of the stimulable phosphor layer with a colorant which is capable of absorbing stimulating rays, so that a radiation image of a high sharpness and a good graininess can be produced.
U.S. Pat. No. 4,574,102 describes varying of a weight ratio of binder to stimulable phosphor particles along the depth of the stimulable phosphor layer, so that a radiation image of a high sharpness can be obtained.
Although the radiation image storage panel is preferred to have high quality in all of sensitivity, sharpness, graininess and the like, it is not easy to prepare a radiation image storage panel which satisfies all of the preferred features. Therefore, a radiation image storage panel is generally designed and produced to have sufficiently high quality in the nature specifically required in radiography for the specific purpose. That is because, in medical diagnosis, a variety of portions of human body are examined, and a variety of requirements are raised to the nature and quality of radiation images depending upon the portions to be examined.
In radiography, it is known that mammography requires a radiation image of an extremely high sharpness so as to easily diagnose mammary cancer.